Capacitor closed relay having reduced holding current



P F. p. SNYDER 2,427,751

CAPACITOR CLOSED RELAY HAVING REDUCED HOLDING CURRENT Original Filedlarch 29, .1945

WITNESSES: INVENTOR Fredmcu'usn du.

BY M TIORNEY Patented 23, 194

UNITED STATES PATENT OFFICE cnraorroa CLOSED RELAY navmcnnnucan nonnmeCURRENT Frederick n. Snyder, Milton, Masa, admin to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Original application March 29, 1945, Serial No. 585,515.Divided and this application Decembet 7, 1940, Serial No. 114,827

My invention relates electromagnetic relays and represents a divisionfrom my copending application Serial No. 585,515, filed-March (29, 1945.

1 claim. (Cl. 175-320) to control systems for It is an object of theinvention to provide relay ii -obtained without the use of a separateself-sealing contact and holding circuit usually required for suchrelays. I I

-Another object of the invention is to devise a low voltage relay whichrequires only a two-wire a control circuit and thereby affordssimplifying the appertaining control system. The latter object, morespecifically, is intended to permit obtaining low voltage protection inmagnetic starters for motors when using a two-wire master control systemfor the motor. Such two-wire control systems are used, for instance,when a limit switch, thermostat or some similarly simple contact deviceis employed for governing the operation of a motor. Two-wire systems forobtaining low voltage control are also of advantage where the controlapparatus proper is installed at a long distance away from a push buttonor the like control contact. In such cases the possibility of affordlnglow voltage protection by means of a twowire relay circuit permitssaving one control wire between the control equipment and theappertaining push button contact.

-In order to achieve the above-mentioned objects and in accordance withmy invention, I interconnect the two input terminals of the relaycircuit by resistance means in series connection with a rectifier and acapacitor so that the capacitor is charged through the resistance meansand the rectifier when the terminals are energized. The relay to becontrolled has a control coil connected across the capacitor; and a,control contact is disposed between the coil and the capacitor. Inconjunction with the just-mentioned circuit arrangement, the resistancemeans and the relay coil are rated relative to each other so that thecontinuous current which flows through the resistance means and coilwhen the control contact is closed, is lower than the pickup valuerequired by the relay coil for closing the relay. It is rurtheressential in conJunction with the above-mentioned requirements that thecapacitor be rated for providing, when the control contact is closed, a.temporary discharge current which fiows through the relay coil andexceeds the critical or pickup'value and hence causes the relay toclose.

It is understood in the foregoing that the electromagnetic relayincorporated in the control system has a marked difierence between thecurrent value necessary for causing the relay to pick up and the minimumvalue of current required for holding the relay in closed condition onceit has picked up. Such a difference exists, for instance, in clappertype relays where the armature gap is large when the relay is indropped-oil condition and is small or fully closed after the relay haspicked up. The above-mentioned conditions are also present in relays ofthe latched-in type in which no continuous holding current is requiredfor securing the relay in the closed position.

, The above-mentioned and other objects and, features of my inventionwill be apparent from the following description in conjunction with theembodiment illustrated in the drawing which represents the circuitdiagram of an ordinary, i. e., nonretentive relay, especially designedfor afiording low voltage protection by means oi! a twowire connection.

According to the drawing, the two wires or terminals Li and L! of theenergizing circuit are cross connected by means of a resistor It inseries with a rectifier I1 and a capacitor Ill. The relay IQ of thissystem is of the nonretentive type. That is, it requires a continuousholding or sealing current in order to be maintained in the closedposition in opposition to its armature bias. The relay field structureis denoted by 20, the appertaining armature by 2|, and the contactassembly of the armature by 23. The control coil 22 of the relay isconnected across the capacitor it through a control contact 24. Theresistor l6 and the coil 22 are rated relative to each other so that thecontinuous current which flows through the coil v22, when the contact 24is closed,

is lower than the current magnitude required for.

closing the relay to pick up. However, when the two terminals areenergized, the capacitor It assumes a charge which upon closure ofcontact 24 is discharged through the coil 22. The current surge exceedsthe pickup value and hence causes the armature 2| to move against thestructure 20. Thereafter the continuous current is effective to hold thearmature closed since its value is sufliciently above the criticalholding value.

In this manner the relay It stays closed as long voltage iailure occursat the terminals oi the system. Upon occurrence of voltage failure, thecontact 24 must first be opened and then reclosed in order to charge thecapacitor II and thereafter discharge it through therelay coil. Theholding effect is produced within the energizing circuit 01' the relaycoil so that no separate sealing contact and sealing circuit arenecessary to achieve low voltage protection.

While I have especially described an embodiment of my invention for usein connection with alternating current circuits. it will be understoodfrom the foregoing that the same devices can also be used for directcurrent, it being merely necessary to omit the rectifier I! in suchcases of application. v

Other modifications and changes as to detail will be apparent t thoseskilled in the art upon the study 01' the foregoing disclosure. I,therefore, wish this specification to be understood chiefly asillustrative while the essential features and scope or my invention areintended to be defined by we claim annexed hereto.

. I claim as my invention:

A relay control system comprising two terminal means [or connection to asingle phase alternating current circuit, a connection between saidterminals having a resistor and a rectifier and a capacitorseries-connected with one another so that said capacitor is charged whensaid terminals are energized, an electro-magnetic relay having arelatively high pickup current value and a relatively low holdingcurrent value and being provided with a control coil connected acrosssaid capacitor, a control contact disposed between said coil and saidcapacitor, said resistor and coil being rated so that the continuouscurrent normallv flowing therethrough when said contact is closed isabove said h'oldlng value and below said pickup value, and saidcapacitor being rated for providing, when said contact is closed, a tem-FREDERICK D. SNYDER.

